This description relates to an optical lens, a light emitting device package using the optical lens and a backlight unit.
A conventional light emitting diode is optically disposed with a domed lens, and light is limitedly distributed to within a predetermined region relative to a central axis. If a liquid crystal display (LCD) backlight unit is manufactured using the light emitting diode, one potential problem is that an even light characteristic cannot be obtained due to light emitting characteristic of the light emitting diode.
It implies that a considerable distance is needed to evenly combine white light radiated from the light emitting diode, making it difficult to obtain a uniform light characteristic from a thin backlight unit. In other words, a backlight unit using a light emitting diode brings about a disadvantage of increasing the thickness of an LCD system.
FIG. 1 illustrates a light path from a lens for lateral light emitting according to the prior art, where a light emitting diode (LED.10) is disposed on a domed lens 20. The domed lens 20 is formed thereon with an inclined conical groove 21 and its side is formed with a V-shaped groove 22.
If light emitted from the LED 10 contacts a surface of the conical groove 21, the light is reflected from the inclined conical groove 21 to be radiated sidewise of the lens. If light contacts the V-shaped groove 22 of the lens 20, the light passes through the lens 20 to be radiated sideways of the lens.
In other words, an LED for laterally emitting (or side-emitting) light (hereinafter referred to as a lateral LED) according to the prior art serves to laterally radiate light emitted from the LED 10 using a lens.
Meanwhile, the injection-molded lens 20 is formed at a region corresponding to an apex 22a of the V-shaped groove 22 with prominences and depressions (unevenness) if closely looked at (for example, in less than a millimeter unit), such that light of the LED 10 emitted from the region is not radiated sideways of the lens 10 but upwards of the lens 10.
FIG. 2 is a schematic perspective view of an LED package of FIG. 1, where the LED is bonded to a slug, and the slug is disposed at sides thereof with leads 31 and 32 which are in turn electrically bonded to the LED.
Furthermore, the LED and the slug are molded by molding means in order to expose a light emitting surface of the LED and the leads 31 and 32, and the lens 20 of FIG. 1 encompassing the LED is bonded to the molding means.
FIG. 3 is a light emitting distribution table of an LED package according to the prior art, where it shows that a large amount of light is radiated sidewise of the package as indicated in ‘a’ and ‘b’ of the distribution table while a small amount of light is radiated through a center of the package.
FIG. 1 implies that although most of the light is radiated sideways of the lens, some of the light is radiated upwards of the lens. In other words, the LED package thus described cannot implement a perfect light emission to lateral surfaces, such that if it is used as a light source for a display, light is partially emitted from the light emitting diode relative to the center of the LED package, resulting in a problem in making a planar light source.
To be more specific, the partial emission of light relative to the center of the LED package results in so-called light irregularity referred to as a hot spot phenomenon where spots are generated about a center of pixels displayed on the display, causing degradation of picture quality on the display. FIG. 4 illustrates in detail one of the causes generating the hot spots.
If the size of a light emitting diode 10 is very small, an amount of light emitted to a lateral surface of a lens by being reflected from a surface 21 of a conical shaped groove according to the prior art increases, but if the size of the light emitting diode 10 is large, light (C) progressing at an angle less than a critical angle from the surface 21 of the conical shaped groove exists to allow the light to be emitted from an upper surface of the lens, thereby generating the hot spot, because the surface 21 of the conical shaped groove totally reflects only the light (A) progressing at an angle larger than the critical angle out of light radiated from the light emitting diode 10.
At this time, light (B) progressing to a lateral surface of the lens is nothing to do with hot spots, as shown in FIG. 4.
FIG. 5 illustrates a cross-sectional view of a light emitting diode packaged in a printed circuit board according to the prior art, where a plurality of lateral light emitting diode packages 50 are packaged in a printed circuit board 60. As mentioned, a printed circuit board packaged with lateral light emitting diode packages is employed for a backlight unit as depicted in FIG. 6.
FIG. 6 is a schematic cross-sectional view of a light emitting diode employed for an LCD backlight unit according to the prior art.
In order to address the problem of the light emitted to the center of the light emitting diode package, an LCD backlight unit is mounted with a hot spot baffle plate 80. In other words, an LCD backlight unit 90 is configured in such a manner that hot spot baffle plates 80 are mounted on each light emitting diode package 70 packaged in the printed circuit board 60, and a light guide plate 85 is disposed on an upper surface of the hot spot baffle plate 80, and an upper surface distanced from the light guide plate 85 is disposed with an LCD 95 to finish the assembly of the backlight unit 90 and the LCD 95.
There is a disadvantage in the backlight unit 90 thus constructed in that a plurality of light emitting diode packages 90 should be mounted thereon with hot spot baffle plates 80 called diverters to complicate the assembly process.
There is another disadvantage in that if there is an erroneous arrangement of the hot spot baffle plates 80 on the plurality of light emitting diode packages 70, spots similar to the hot spots are generated on a screen of a final display. Still another disadvantage is that thickness of the display panel increases as much as that of the hot spot baffle plate 80.